The present invention relates to a technique for preventing the unauthorized copying of proprietary application-specific integrated circuit (ASIC) designs. Specifically, a method and circuit is described which when used in designing ASIC circuits produces a circuit whose function has a limited lifetime.
The integrated circuit business includes a significant market for producing custom integrated circuits for various applications. The industry creates these ASIC components through a cooperative venture between the ASIC supplier and the customer who defines a design to be implemented in an ASIC. A course of business has developed between the manufacturer and customer which permits the ASIC design to be implemented using a core circuit defined by the manufacturer, which the customer then adapts to his own proprietary circuit designs. Using a hardware descriptive language, the manufacturer defines a core circuit which the customer will add to his proprietary circuitry. The basic circuit definitions created by the manufacturer are then given to the customer for use in creating the complete ASIC design. The core may be either a hard core, which represents the physical layout of the basic core circuitry around which the customer designs his proprietary circuitry, or a software model, or soft core, which defines the basic circuit of the manufacturer to which the customer adds his proprietary circuitry.
The soft core represents a compilation of a net list which defines the elements and interconnection between elements to carry out a basic circuit function. The compiled net list may be further encrypted by the manufacturer using standard public key encryption methods, and supplied to the user. The user may then encrypt the net list so that it may be further augmented using the hardware descriptive language to define connections between the circuitry and the user's proprietary circuitry. The completed design is returned as an encrypted net list to the manufacturer, who can then create the various masks to implement the ASIC in silicon.
The considerable design effort in these core circuit designs are vulnerable to theft or unauthorized use by other outside manufacturers to implement a customer's ASIC design. The disclosed net list of the core circuitry permits its disclosure to others who may copy the net list, and otherwise take possession of the manufacturer's core designs. The present invention provides the ability to protect a soft core from copying by others, while still permitting the customer to have the ability to modify the soft core in a design which can be manufactured by the legitimate manufacturer.